U.S. patent number 3,673,303 [Application Number 05/068,748] was granted by the patent office on 1972-06-27 for voltage generating device for controlling musical tone output from electronic musical instruments.
This patent grant is currently assigned to Nippon Gakki Seizo Kabushiki Kaisha. Invention is credited to Hiroshi Amano.
United States Patent |
3,673,303 |
Amano |
June 27, 1972 |
VOLTAGE GENERATING DEVICE FOR CONTROLLING MUSICAL TONE OUTPUT FROM
ELECTRONIC MUSICAL INSTRUMENTS
Abstract
There is disclosed a voltage generating device of compact
structure for controlling musical tone output signals from an
electronic keyboard musical instrument to a level corresponding to
the magnitude of a key depressing force or the velocity with which
the key is depressed. Below the keyboard is positioned a
non-magnetic case which supports two parallel magnetic cores and a
magnet disposed therebetween which are common to a plurality of
keys, and on at least one of the two magnetic cores there are
fitted a plurality of coils in a manner that the coils correspond
to the respective keys. There is mounted on the underside of each
key a magnetic material constituting a magnetic circuit along with
the two magnetic cores and the magnet received in the case. On
depressing a key, the magnetic material mounted on the key is drawn
near the two magnetic cores to generate in the coil a voltage
having a level corresponding to the velocity with which the key is
depressed, the voltage being used in controlling the corresponding
musical tone output signal.
Inventors: |
Amano; Hiroshi (Hamamatsu,
JA) |
Assignee: |
Nippon Gakki Seizo Kabushiki
Kaisha (Hamamatsu-shi, JA)
|
Family
ID: |
13804578 |
Appl.
No.: |
05/068,748 |
Filed: |
September 1, 1970 |
Foreign Application Priority Data
|
|
|
|
|
Sep 3, 1969 [JA] |
|
|
44/83514 |
|
Current U.S.
Class: |
84/688; 84/718;
84/DIG.7; 984/319 |
Current CPC
Class: |
G10H
1/0555 (20130101); Y10S 84/07 (20130101) |
Current International
Class: |
G10H
1/055 (20060101); G10h 001/00 () |
Field of
Search: |
;84/1.01,1.15,1.24,1.26D |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Myers; Lewis H.
Assistant Examiner: Weldon; U.
Claims
What is claimed is:
1. For use in a keyboard type electronic musical instrument, a
voltage generating arrangement for producing electrical signals in
response to depression of the keys comprising in combination:
a plurality of keys arranged side by side, each supported so as to
allow one end thereof to rock vertically in a conventional musical
keyboard arrangement;
an elongated non-magnetic housing positioned beneath said keys in a
plane substantially parallel thereto and extending substantially
transversely of the longitudinal axes of the individual keys;
a pair of elongated magnetic core members supported in spaced
parallel relation to each other within said housing, at least one
of said core members having a plurality of spaced parallel pole
piece projections equal in number to the number of keys;
a plurality of coils, one wound around each of said pole piece
projections;
an elongated first member of magnetic material received within said
housing, positioned between and in contact with the lower portion
of said core members and defining therewith a substantially channel
shaped magnetic circuit, the open side of said channel facing
vertically upwardly toward the underside of said keys;
a second member of magnetic material attached to the underside of
each of the keys, one of said first and second magnetic members
being a permanent magnet;
whereby when anyone of said keys is depressed, a voltage is
generated in the corresponding coil and the magnitude of said
voltage is a function of the speed with which the key is
depressed.
2. The voltage generating device according to claim 1 wherein said
housing is supported at one end by a keyboard supporting frame and
at the other end by a stopper member for regulating the range of
key depression.
3. The voltage generating device according to claim 2 wherein said
housing is supported by the keyboard supporting frame by means
capable of varying the position of the case with respect to the
keyboard.
4. The voltage generating device according to claim 1 wherein said
housing has partition walls jointly defining a rectangular space
set up on the bottom plate thereof; said first and second magnetic
cores are received in said case in such a manner as to extend along
the inner surfaces of the opposite longitudinal partition walls;
said first member is interposed between said two magnetic cores in
close contact therewith; and a corrugated plate spring inserted
into the space defined between at least one of said magnetic cores
and the inner surface of one of the opposite longitudinal partition
walls.
5. The voltage generating device according to claim 4 wherein at
least two projecting rods are erected at that part of the bottom
plate of said case which is defined by its partition walls so as to
be arranged in a straight line with a predetermined spacing in the
direction of key arrangement; and said first member is perforated
with at least two apertures similarly arranged in a straight line
in the direction of key arrangement with the same spacing at which
said projecting rods are disposed, said apertures allowing said
projecting rods to pass therethrough thereby securely to fix said
first member.
6. The voltage generating device according to claim 1 wherein the
magnetic core other than the magnetic core fitted with said coils
is perforated with at least one aperture, and a retaining plate
having at least one first engaging strip integrally formed
therewith and fitted into said aperture and at least one second
engaging strip integrally formed therewith and inserted into the
interspace between the adjacent projections formed on said magnetic
core, whereby the fitting of said first engaging strip into said
aperture and the insertion of said second engaging strip into the
interspace between the adjacent projections formed on said latter
magnetic core enable said first member to be securely held in
place.
7. The voltage generating device according to claim 1 wherein each
of said second members are bent at both ends to form two leg
members extending in slightly offsetting relationship with respect
to said two magnetic cores respectively, whereby, when each of said
keys is depressed halfway said two leg members are drawn closest to
said two magnetic cores.
8. The voltage generating device according to claim 7 wherein one
of said two leg members which is positioned closer to the point at
which each of said keys is supported has a greater length than the
other, and one of said magnetic cores which corresponds to the
longer leg member has a smaller height than the other which
corresponds to the shorter leg member, so that, upon key
depression, the two leg members can approach simultaneously said
two magnetic cores with a substantially equal space
therebetween.
9. The voltage generating device according to claim 1 wherein each
of said second members has two projecting cutout strips
corresponding to said first and second magnetic cores respectively,
so that when each of said keys is depressed halfway, the projecting
cutout strips approach closest to said first and second magnetic
cores.
10. The voltage generating device according to claim 1 wherein each
of said second members is perforated with two apertures facing said
first and second magnetic cores, so that when each of said keys is
depressed halfway, each of said second members is drawn nearest to
said first and second magnetic cores, and upon further key
depression, said first and second magnetic cores enter said two
apertures respectively.
11. The combination defined by claim 1 in which said first members
are permanent magnets.
12. The combination defined by claim 1 in which said second members
are permanent magnets.
Description
BACKGROUND OF THE INVENTION
The present invention relates to an electronic musical instrument
and more particularly to an electronic musical instrument provided
with a voltage generating device for controlling musical tone
output signals therefrom in accordance with the magnitude of a key
depressing force.
With a keyboard musical instrument other than an electronic musical
instrument, for example, a piano, there arises a prominent
difference in the volume of musical tones obtained between the case
where the key is strongly, or quickly depressed and the case where
they key is lightly or slowly depressed.
However, with the conventional electronic musical instrument, for
example, an electronic organ, when a key is depressed, it only
causes a key switch associated therewith to be closed and signals
from a tone generator corresponding to the key to be conducted to
another prescribed circuit. Accordingly, key depression, whether
effected quickly or slowly, does not give rise to any change in
tones, namely, a mere key operation fails to produce a diversified
performance.
It is therefore preferred that an electronic musical instrument
such as an electronic organ, be provided with means for detecting
the magnitude of a key depressing force or more precisely the
velocity with which the key is depressed, thereby to control
musical tone output signals and particularly desired that such
means be installed in position below the keys arranged at a small
space.
SUMMARY OF THE INVENTION
It is, accordingly, an object of this invention to provide a
voltage generating device for controlling musical tone output
signals which is of sufficiently compact construction to be
installed in position below a plurality of keys.
It is another object of this invention to provide the aforesaid
device being capable of quickly controlling the volume of musical
tones to a value corresponding to the magnitude of a key depressing
force, when a key is depressed.
The control voltage generating device of the present invention
comprises movable magnetic materials or magnets fitted to the
undersides of the respective keys; two magnetic cores disposed
below the keyboard so as to extend in the direction of key
arrangement, at least one of which is provided on one side with a
plurality of projections arranged at a prescribed interval, the
projections corresponding to the respective keys; a magnet or
magnetic material positioned between the magnetic cores; a case of
non-magnetic material for receiving the magnetic cores and the
stationary magnet or magnetic material interposed therebetween; and
coils wound around the respective projections. When a key is
depressed, the movable magnetic material or magnet mounted on its
underside is drawn near the two magnetic cores to induce into the
coil associated with the depressed key a voltage based on the
changed magnetic flux corresponding to the magnitude of a key
depressing force or the velocity with which the key is depressed,
and the voltage is supplied to control a variable attenuator
cascade connected to the tone generator.
Another feature of the present invention is that the movable
magnetic material or magnet mounted on the underside of the key
assumes such a shape that when a key is depressed half way, it is
drawn nearest to the two magnetic cores, enabling musical tone
output to be produced immediately upon key depression with a level
corresponding to the magnitude of a key depressing force.
BRIEF EXPLANATION OF THE DRAWINGS
FIG. 1 is a schematic side view, partly in section, of the keyboard
mechanism of an electronic organ provided with a control voltage
generating device according to an embodiment of the present
invention;
FIG. 2 is a similar side view to that of FIG. 1 at the time of key
depression;
FIG. 3 is an exploded perspective view of the major parts of the
control voltage generating device of the present invention;
FIGS. 4A and 4B are schematic side views illustrating the operation
of the control voltage generating device of the present
invention;
FIGS. 5A and 5B jointly present a circuit for controlling musical
tones by output signals from the control voltage generating device
of the present invention;
FIGS. 6A and 6B indicate wave forms used for illustrating the
operation of the circuits of FIGS. 5A and 5B;
FIG. 7 is a curve diagram showing the relationship of the depressed
position of the key and the magnitude of magnetic flux passing
through the magnetic cores at the key depression;
FIGS. 8A, 8B and 8C are schematic side views, partly in section,
illustrating the operation of a control voltage generating device
according to another embodiment of the invention;
FIG. 9 is a schematic side view, partly in section, of a control
voltage generating device according to still another embodiment of
the invention; and
FIG. 10 is a schematic side view, partly in section, of a control
voltage generating device according to a further embodiment of the
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In FIGS. 1 and 2, the reference numeral 1 represents the body of
one of a plurality of keys constituting the keyboard of an
electronic musical instrument, which are arranged side by side at a
small space in a direction perpendicular to the plane of the paper.
The key body 1 is made of, for example, plastics material, and to
the rear part of the key body (opposite to that part of the key
body at which it is depressed) is fixedly secured a key arm 2
formed of magnetic material, for example, cold rolled steel plate
or ferrite, the arm extending in the longitudinal direction of the
key body 1. While, in this embodiment, the key body 1 and key arm 2
constitute a key, the key body 1 is referred to as a key by way of
simplification. Of course, the key body 1 and key arm 2 may be
integrally prepared from plastics material, and there may be
attached a magnetic material to the underside of that part of the
key corresponding to the key arm. The rear end of the key arm 2 is
rotatably supported, as is well known, by a supporting plate 3
fixed to the rear end of a keyboard supporting frame 4. Between the
rear end of the key arm 2 and one end of the supporting plate 3 is
disposed a spring 5 for keeping the forward end of the key 1
upwardly urged. On the underside of forward end of the key 1 is
formed a downwardly projecting stopper section 8.
The stopper section 8 has a member 10 integrally fitted thereto,
the upper surface of which faces the end plane 9 of the stopper
section 8. Between the member 10 and the end plane 9 of the stopper
section 8 is positioned a stopper member 12, both sides of which
are fitted with a buffer member 13 permissibly made of felt. This
stopper member 12 is intended to define the range within which the
key 1 is allowed to rock vertically. To the underside of the key
arm 2 is fitted an actuating rod 14 in such a manner as to
penetrate the keyboard supporting frame 4 and the bottom of a
switch box 15 mounted under the keyboard supporting frame 4. In the
switch box 15 are provided a group of movable contact strips 16
penetrating the actuating rod 14 and a plurality of fixed contact
strips 17 disposed near the ends of the movable contact strips 16.
When a key is depressed, there is produced a musical tone signal
having a desired tone color by the tone generator associated with
the depressed key. Below the switch box 15 is placed a switch 18
which, upon key depression, is operated by the actuating rod 14 to
operate the later described control circuit. Between the keyboard
supporting frame 4 and stopper member 12 is disposed a case 20
housing the major part of a device for generating a control
voltage. The case 20 is disposed between one end of the keyboard
supporting frame 4 through an adjustable spring 19 and one end of
the stopper member 12. The voltage generating device is shown in
detail in FIG. 3.
The case 20 is formed of a non-magnetic material, for example,
rubber or plastics material. The case 20 has upwardly projecting
partition walls 23 jointly defining a rectangular space set up at
the central part between the opposite longitudinal sections 21 and
22 of the bottom plate and two projecting rods 24 and 25 arranged
at a prescribed space along the central line of the area defined by
the partition walls 23. In the case 20 are placed two magnetic
cores extending along the inner surfaces of the longitudinal
partition walls 23, that is, a first magnetic core 26 assuming a
combed shape which is provided on the upper edge with a plurality
of projections 27 arranged at a prescribed space so as to
correspond to the respective keys and a second magnetic core 28
formed into a flat plate which is perforated with two rectangular
apertures 29 disposed at a prescribed space along the longitudinal
central line. These two cores 26 and 28 consist of a magnetic
material such as iron or barium ferrite and have substantially the
same length as the inner surface of the longitudinal partition
walls 23 and a mutually equal height. Further along the
longitudinal central line of the bottom plate of the case 20 and
between the magnetic cores is placed a permanent magnet 30
perforated with two apertures 31 spaced from each other at the same
interval as the aforesaid projecting rods 24 and 25 of the case 20,
the projecting rods 24 and 25 being fitted into the apertures 31.
The permanent magnet 30 assumes a rectangular cross section and has
substantially the same length as the two magnetic cores 26 and 28
disposed along the inner surfaces of the longitudinal partition
walls 23 and a sufficient width closely to contact them. The
magnetic poles of the permanent magnet 30 are so oriented as to
face the magnetic cores 26 and 28 respectively. The permanent
magnet 30 is pressed downward by a retaining plate 32. The
retaining plate 32 of substantially the same length and width as
the permanent magnet 30 has a pair of first engaging strips 33 to
be inserted into the two rectangular apertures 29 of the second
flat plate magnetic core 28, and a pair of second engaging strips
34 to be fitted into the interspace between the adjacent
projections of the first comb-shaped magnetic core 26, and further
two apertures 35 formed at the same space as the two projecting
rods 24 and 25 of the supporting case 20.
Engagement of the first engaging strips 33, second engaging strips
34 and two apertures 35 of the retaining plate 32 with the
corresponding parts permits the permanent magnet 30 to be securely
set in the supporting case 20. The heads of the projecting rods 24
and 25 of the supporting case 20 which rise above the plate 32 are
pressed flat by, for example, being properly heated, thereby
causing all the parts to be tightly held in the supporting case 20.
Referring to the first and second engaging strips 33 and 34 of the
retaining plate 32, it will be sufficient if there is formed at
least one of these first and second strips.
There is fitted a bobbin 36 having a coil 37 wound thereabout on to
the projections 27 of the comb-shaped magnetic core 26. Both
terminals 38 and 39 of the coil 37 are connected to the terminals
40 provided outside of the partition walls 23 on the longitudinal
section 21 of the bottom plate of the case 20. The latter terminals
40 are connected to the later described control circuit.
As mentioned above, the supporting case 20 is fixed to the stopper
member 12 and the keyboard frame 4 at its opposite longitudinal
sections 21 and 22 using proper means. If, in this case, one of
said fixing means consists of, for example, the adjustable spring
19 so as to cause the supporting case 20 to have a changeable
vertical position with respect to the key arm 2, then it is
possible minutely to control an electromotive force generated in
the coil upon key depression, thus offering great advantage.
To assure the tight contact of the first and second magnetic cores
26 and 28 through the permanent magent 30 interposed therebetween,
it is preferred that there be interposed a corrugated plate spring
41 between one of the magnetic cores 26 and 28 and the inner
surface of one of the longitudinal partition walls 23. It is also
possible to use, if necessary, other fixing means than described
above in order firmly to hold the parts received in the supporting
case 20. In the foregoing embodiment, only the first magnetic core
26 is formed into a combed shape, but the second magnetic core 28
may also assume a similar combed shape. In this case, it is
possible to fit coil bobbins having coils on to the mutually facing
projections of both magnetic cores 26 and 28, connect the coils of
the bobbins in series, thereby using the total sum of voltages
drawn out of the coils as a control voltage.
There will now be described the operation of a keyboard mechanism
involving the voltage generating device of the present invention
constructed as described above. FIG. 1 represents the normal
position of the key 1 when it is not depressed. Under this
condition, there is not produced any musical tone signal. Since, in
this state, no magnetic circuit is formed between the permanent
magnet 30, the first and second magnetic cores 26 and 28, and the
key arm 2 of a magnetic material, with air gaps prevailing between
the key arm 2 and the magnetic cores 26 and 28, there is not
generated any voltage in the coil 37. Since most of the magnetic
flux from the permanent magnet 30 leak as illustrated in FIG. 4A,
there is also produced no attractive force between the key arm 2
and the permanent magnet 30.
Depression of the key 1 brings about the condition of FIG. 2. Now
the actuating rod 14 is brought down, causing the movable contact
strip 16 to contact the fixed contact strip 17 to draw out of the
tone generator a signal having a pitch corresponding to the
depressed key 1. Further, the switch 18 is closed to actuate the
control circuit. On the other hand, the key depression breaks up
the normal state of the aforesaid magnetic circuit, closing the
magnetic circuit and varying the magnetic flux flowing through the
magnetic cores 26 and 28, so as to generate in the coil 37
associated with the depressed key an electromotive force
corresponding to the magnitude of a key depressing force or more
precisely the velocity with which the key is depressed. The
electromotive force e may be expressed by the following
equation:
e = n .sup.. (d/dt)
where: n = number of coil windings
.PHI. = magnetic flux passing through a coil The magnetic flux
reaches a maximum when the depressed key is brought to its final
position as shown in FIG. 4B where the magnetic resistance due to
air gaps is minimum. However, the maximum attractive force exerted
by the permanent magnet 30 at this time is so designed as to be
smaller than the tensile force of the spring 5. Accordingly, when
the key is released from its depressed position indicated in FIGS.
2 and 4B, then the key will be brought back to its original
position illustrated in FIGS. 1 and 4A.
The electromotive force e generated in the coil 37 is used as a
voltage for controlling musical tone output signals. While there
may be contemplated various types of musical tone controlling
circuit, there will now be described two examples of such circuit
presented in FIGS. 5A and 5B. Throughout these figures, the voltage
generating device is indicated as a moving magnet type. While the
embodiment of FIG. 1 involved a variable reluctance type of voltage
generator in which the magnet was fixed in a supporting case 20
made of non-magnetic material and the magnetic material of the key
arm 2 was made movable, the type may be easily converted to a
moving magnet type by replacing the permanent magnet 30 received in
the supporting case 20 with a magnetic material and mounting on the
underside of the key arm 2 a permanent magnet whose poles are
oriented in the longitudinal direction of the key. The variable
reluctance type and moving magnet type of voltage generating device
have the undermentioned advantages over the moving coil type.
Referring to FIG. 5A, the reference numeral 50 denotes a moving
magnet fitted to a key so as to move in the direction of the arrow.
51 is a magnetic core having a coil 52 wound thereabout. One end of
the coil 52 is grounded and the other is connected to the anode of
a diode 53. Across a serial circuit including the coil 52 and the
diode 53 is connected a capacitor 54. To the capacitor 54 is
connected in parallel a serial circuit consisting of a resistor 55
and normally closed contact 56. Where the diode 53 is connected as
shown in FIG. 5A, the juncture of the diode 53 and the capacitor 54
is supplied with a positive voltage alone. The voltage is used in
controlling a variable attenuator 57 cascade connected to a tone
generator 58. Output from the variable attenuator 57 is conducted
to a prescribed circuit.
There will now be described the operation of the aforesaid control
circuit. When the key is depressed the magnet 50 moves to the coil
52 to induce thereinto an electromotive force e corresponding to
the magnitude of a key depressing force indicated by the
aforementioned formula. The electromotive force e is rectified by
the diode 53 to charge the capacitor 54. The normally closed
contact 56 is included in the switch 18 disposed below the switch
box 15 shown in FIG. 1 and, upon key depression, is opened by the
actuating rod 14 to keep the capacitor 54 continuously charged with
a voltage corresponding to the electromotive force e until the key
is released from depression. When the key depression comes to an
end, the normally closed contact 56 which has been opened up to
this point is closed to cause the voltage charged into the
capacitor 54 to be discharged through the resistor 55. The charged
voltage of the capacitor 54 is supplied to the variable attenuator
57 to control signals from the tone generator 58 to a level
corresponding to the magnitude of a key depressing force or the
velocity with which the key is depressed. The variable attenuator
57 may consist of a filed effect transistor shown in FIG. 5B.
The numerals 71 and 72 of FIG. 6A represent the wave forms of
control D.C. signals from the control circuit having voltage levels
corresponding to different magnitudes of a key depressing force.
The numerals 73 and 74 of FIG. 6B indicate the patterns of musical
tone outputs from the variable attenuator 57 having levels
corresponding to the control voltages 71 and 72. Normally, when a
key is not depressed, the variable attenuator 57 is, of course,
prevented by, for example, a key switch means (not shown) from
being supplied with musical tones from the tone generator 58.
FIG. 5B is a modification of the circuit arrangement shown in FIG.
5A. The voltage generated in the coil 52 is conducted through a
capacitor 59 to a transistor amplifier 60 and the amplified output
is rectified by the diode 53. The rectified voltage or control
voltage charged into the capacitor 54 is supplied to the gate
electrode of the variable attenuator 57 consisting of a field
effect transistor 61 to vary its internal resistance. As the gate
electrode of the field effect transistor 61 is supplied with
increasing control voltage, its internal resistance decreases to
permit a larger output of musical tones. The source electrode of
the field effect transistor 61 is connected through a capacitor 62
to a tone generator 58 and grounded through a resistor 63. The
drain electrode of the transistor 61 is connected through a
capacitor 64 to a prescribed circuit, and grounded through a
resistor 65. The control circuit of FIG. 5B performs the same
operation as that of FIG. 5A, excepting that the voltage generated
in the coil 52 is amplified by the amplifier 60. The same parts of
FIG. 5B as those of FIG. 5A are denoted by the same numerals and
description thereof is omitted.
The object and operation of the control voltage generating device
according to the present invention will be apparent from the
foregoing description.
Now let us consider in detail by reference to FIGS. 4A and 4B the
characteristics of the voltage generating device used in the
embodiment of FIG. 1. After key depression, the magnetic flux
flowing through the magnetic cores 26 and 28 gradually increases
and reaches a maximum when the key is brought to the most depressed
position where the key arm 2 is drawn closest to the magnetic cores
26 and 28 as shown in FIG. 4B. This relationship is represented by
the curve a of FIG. 7.
As apparent from this figure, the magnetic flux little varies at
the initial stage of key depression, but gradually increases as the
depression approaches its end. Accordingly, the electromotive force
generated in the coil 52 is small at the initial stage of key
depression, but gradually grows large toward the end of the
depression. At the initial stage of key depression, therefore,
there is only obtained a small control voltage, permitting a little
or no output of musical tones, whereas when the key is fully
depressed, the control voltage increases to permit a large output
of musical tones. This will, however, result in an appreciable
delay in the rise of musical tone signals derived from key
depression during the performance of an electronic musical
instrument. Particularly where performance is to be made at quick
tempo, the player will feel considerable difficulties in playing
the instrument.
In view of such fact, the present invention has further developed
other embodiments illustrated in FIGS. 8, 9 and 10 which are so
designed as to obtain immediately after key depression musical tone
output signals having a voltage level corresponding to the
magnitude of a key depressing force. The same parts of these
figures as those of FIG. 1 are denoted by the same numerals and
description thereof is omitted.
Referring to FIGS. 8A, 8B and 8C, the key arm 2 fitted to the
underside of the rear end portion of the key 1 may consist of a
proper kind of metal or plastics material capable of being
integrally formed with the body of the key 1. Of the two magnetic
cores 26 and 28 received in the supporting case 20, the first
magnetic core 26 disposed near the front side of the key and fitted
with the coil 37 has a greater height than the second magnetic core
28. To the underside of the key arm 2 is fixed by suitable means,
for example, screws 83 an induced iron piece 80 having two leg
members 81 and 82 formed by bending both ends thereof substantially
at right angles to the main body in such a manner as to cause the
two leg members 81 and 82 to face the magnetic cores 26 and 28
respectively in slightly offsetting relationship with respect
thereto. Of the two leg members 81 and 82 of the induced iron piece
80, the leg member 82 facing the second magnetic core 28 having a
smaller height than the first magnetic core 26 is formed longer
than the other leg member 81 facing the first magnetic core 26
having a greater height than the second magnetic core 28, so that
at the time of key depression, these two leg members 81 and 82
approach simultaneously the first and second magnetic cores 26 and
28 with an equal space therebetween. The aforementioned arrangement
permits the two leg members 81 and 82 of the induced iron piece 80
to approach closest to the magnetic cores 26 and 28 when the key is
depressed substantially half way as shown in FIG. 8B. At this time
the magnetic flux passing through the magnetic cores 26 and 28
attains a maximum value shown by the curve b of FIG. 7, so that an
electromotive force generated in the coil 37 also grows largest.
Where the key is most depressed as shown in FIG. 8C, the leg
members 81 and 82 of the induced iron piece 80 are removed from the
first and second magnetic cores 26 and 28, so that the magnetic
flux travelling therethrough is reduced with the resultant decrease
of the electromotive force induced into the coil 37. As apparent,
however, from the aforementioned two control circuits, the control
voltage supplied to the variable attenuator 57 upon key depression
is derived from the voltage charged into the capacitor 54 which has
a level corresponding to the electromotive force induced into the
coil 37 upon key depression. Under the arrangement of FIG. 8,
therefore, the control voltage resulting from the maximum
electromotive force obtained when the key is depressed
substantially half way is conducted to the variable attenuator 57
even after key depression is finished. According to the embodiment
of FIG. 8, therefore, there occurs a far less delay in the rise of
musical tone output signals than in the embodiment of FIG. 2, thus
permitting a quick tempo performance to be carried out easily. With
the embodiment of FIG. 8, the induced iron piece 80 may of course
be replaced by a magnet having the same form. In this case, the
permanent magnet 30 received in the supporting case 20 may also be
substituted by a magnetic material.
FIG. 9 is a modification of the embodiment of FIG. 8. According to
the embodiment of FIG. 9, the key arm 2 of FIG. 1 made of magnetic
material has two projecting cutout strips 91 and 92 which
functionally correspond to the aforesaid two leg members 81 and 82
of the induced iron piece 80 of FIG. 8. Under such arrangement, the
projecting output strips 91 and 92 of the key arm 2 are drawn
nearest to the magnetic cores 26 and 28 respectively when the key
is depressed substantially half way between the position (indicated
by a broken line) where the key stands at rest and the position
(indicated by a solid line) where the key finishes its depression,
thus serving the same purpose as the embodiment of FIG. 8. In this
case, the ends of the magnetic cores 26 and 28 may, upon key
depression, be inserted into the apertures 93 and 94 resulting from
the formation of the projecting output strips 91 and 92. With this
embodiment, the key arm may, of course, be replaced by a magnet and
the permanent magnet in the supporting case 20 may also be
substituted by a magnetic material.
In the embodiment of FIG. 10, the key arm 2 made of magnetic
material is simply perforated with two apertures 95 and 96 instead
of being provided with projecting cutout strips as in FIG. 9. At
the initial stage of key depression, the ends of the magnetic cores
26 and 28 approach the peripheral surfaces of the apertures 95 and
96 and thereafter are inserted thereinto, permitting the further
depression of the key. Like the embodiments of FIGS. 8 and 9, the
embodiment of FIG. 10 quickens the rise of musical tone output
signals derived from key depression. With this embodiment, the key
arm may, of course, be replaced by a magnet and the permanent
magnet in the supporting case 20 may also be substituted by a
magnetic material.
As mentioned above, according to this invention, a non-magnetic
case supporting two magnetic cores and magnet or magnetic material
disposed therebetween which are common to a plurality of keys is
disposed below the keys, and separate coils corresponding to the
respective keys are fitted on to at least one of the magnetic
cores. Accordingly, the present controlling voltage generating
device is of compact construction and saves space effectively with
respect to the keyboard in which there are arranged a plurality of
keys at a small interval.
Further, since the elements constituting the magnetic circuit are
separated into movable and fixed parts, the voltage generating
device can be easily assembled. According to the present invention,
if the coil used as a detection element is fixed, it is less
subject to damage due to abnormal vibrations or shocks than in the
moving coil type, so that it withstands a semipermanent use.
With the prior art electronic musical instrument, the keys undergo
and appreciably great pressure exerted by the return spring
attached thereto and various contacts within the switch box,
rendering the key touch unduly heavy. In contrast, the electronic
musical instrument of the present invention has the advantage that
the key touch feels light due to an attractive force arising
between the key and the magnet upon key depression.
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